有时咱们在查询某个实体的时候，给定的条件是不固定的，这是咱们就须要动态 构建相应的查询语句，在JPA2.0中咱们能够经过Criteria接口查询，JPA criteria查询.相比JPQL,其优点是类型安全,更加的面向对象.而在Spring data JPA中相应的接口是JpaSpecificationExecutor，这个接口基本是围绕着Specification接口来定义的。 Specification接口中只定义了以下一个方法：web
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Predicate toPredicate(Root<T> root, CriteriaQuery<?> query, CriteriaBuilder cb);
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咱们只须要重写这个方法便可，相关知识请自行查阅JPA Criteria查询 spring
过滤条件sql
1：过滤条件会被应用到SQL语句的FROM子句中。在criteria 查询中，查询条件经过Predicate或Expression实例应用到CriteriaQuery对象上。安全
2：这些条件使用 CriteriaQuery .where 方法应用到CriteriaQuery 对象上less
3：CriteriaBuilder也做为Predicate实例的工厂，经过调用CriteriaBuilder 的条件方法（ equal，notEqual， gt， ge，lt， le，between，like等）建立Predicate对象。ide
4：复合的Predicate 语句能够使用CriteriaBuilder的and, or andnot 方法构建。post
相关代码以下，在这个例子中咱们定义了2个类Articel和User类ui
Article:spa
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@Entity
@Table(name = "t_article")
public class Article implements Serializable{
private static final long serialVersionUID = 6112067846581696118L;
@Id
@GeneratedValue
private Integer aid;
private String title;
@Temporal(TemporalType.TIMESTAMP)
private Date postTime;
@Temporal(TemporalType.TIMESTAMP)
private Date lastEditTime;
private String ip;
private String tag;
private boolean forbidComment;//禁止评论
@ManyToOne
@JoinColumn(name = "uid")
private User user;
private boolean recommend;//是不是推荐
@Temporal(TemporalType.TIMESTAMP)
private Date recommendTime;//推荐时间
//setter/getter略
}
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User:code
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@Entity
@Table(name = "t_user")
public class User implements Serializable {
private static final long serialVersionUID = 3703405133265901053L;
@Id
@GeneratedValue
private Integer uid;
private String nickname;
private String password;
//setter/getter略
}
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其中user和article是一对多的关系，是单向的
封装的查询实体SearchArticle
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public class SearchArticle implements Serializable{
private static final long serialVersionUID = -1082122462716689486L;
private int page = 1;
private int limit;
@DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME,pattern = "yyyy-MM-dd HH:mm:ss")
private Date postTimeStart;
@DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME,pattern = "yyyy-MM-dd HH:mm:ss")
private Date postTimeEnd;
@DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME,pattern = "yyyy-MM-dd HH:mm:ss")
private Date recTimeStart;
@DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME,pattern = "yyyy-MM-dd HH:mm:ss")
private Date recTimeEnd;
private String nickname;
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下面是查询方法
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@Autowired
private ArticleRepository articleRepository;
@Override
public QueryResult<ArticleModel> findArticle(SearchArticle searchArticle) {
Sort sort = new Sort(Sort.Direction.DESC,"postTime");
Specification<Article> specification = getWhereClause(searchArticle);
Page<Article> all = articleRepository.findAll(specification, new PageRequest(searchArticle.getPage() - 1, searchArticle.getLimit(),sort));
QueryResult<ArticleModel> result = new QueryResult<>();
List<ArticleModel> list = new ArrayList<>(searchArticle.getLimit());
for (Article article:all.getContent()){
ArticleModel model = new ArticleModel(article.getAid(),article.getTitle(),article.getPostTime(),article.isRecommend(),
article.getRecommendTime(),article.getIp(),article.getUser().getUid(),article.getUser().getNickname());
list.add(model);
}
result.setRows(list);
result.setTotal(all.getTotalElements());
return result;
}
/**
* 动态生成where语句
* @param searchArticle
* @return
*/
private Specification<Article> getWhereClause(final SearchArticle searchArticle){
return new Specification<Article>() {
@Override
public Predicate toPredicate(Root<Article> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
List<Predicate> predicate = new ArrayList<>();
if(searchArticle.getPostTimeStart()!=null){
predicate.add(cb.greaterThanOrEqualTo(root.get("postTime").as(Date.class), searchArticle.getPostTimeStart()));
}
if(searchArticle.getPostTimeEnd()!=null){
predicate.add(cb.lessThanOrEqualTo(root.get("postTime").as(Date.class), searchArticle.getPostTimeEnd()));
}
if(searchArticle.getRecTimeStart()!=null){
predicate.add(cb.greaterThanOrEqualTo(root.get("recommendTime").as(Date.class), searchArticle.getRecTimeStart()));
}
if (searchArticle.getRecTimeEnd()!=null){
predicate.add(cb.lessThanOrEqualTo(root.get("recommendTime").as(Date.class), searchArticle.getRecTimeEnd()));
}
if (StringUtils.isNotBlank(searchArticle.getNickname())){
//两张表关联查询
Join<Article,User> userJoin = root.join(root.getModel().getSingularAttribute("user",User.class),JoinType.LEFT);
predicate.add(cb.like(userJoin.get("nickname").as(String.class), "%" + searchArticle.getNickname() + "%"));
}
Predicate[] pre = new Predicate[predicate.size()];
return query.where(predicate.toArray(pre)).getRestriction();
}
};
}
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其中的 ArticleRepository接口以下，spring data jpa不须要你本身实现dao的接口
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public interface ArticleRepository extends JpaRepository<Article,Integer>,JpaSpecificationExecutor<Article> {}
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经过以上的步骤，咱们就能构建相应的查询sql了，使用这个接口要对JPA2.0中Criteria查询有必定的了解